[avar]

    > Right now, if North Korea launched a missile
    > at California, Japan would have to watch as
    > it sailed over Tokyo.

This doesn't detract from your general point, but I was curious to see if this particular thing was true.

If you use the "measure distance" tool on Google Maps you can see that even if North Korea launched an ICBM from the southernmost part of their eastern coast to the southernmost part of California it would only intersect Japanese territory by a few miles, at the point of Rebun Island northwest of Hokkaido, something they could trivially avoid. They'd have a much bigger practical problem with having to fly it over Russia than Japan.

In order for its course to go anywhere near Tokyo they'd have to be aiming said ICBM somewhere midway around Argentina, around a thousand miles south of Buenos Aires or so.

Don't let the Mercator projection interfere with your sense of reality.